In vivo loading data is to be obtained from specially instrumented total hip and total knee joint replacements. Both the total knee and the total hip joint will contain all the necessary electronic components within the femoral component. The total hip prosthesis will use five channels of AM-FM multiplexed telemetry, while the total knee prosthesis will use five channels of AM-FM telemetry per condylar structure. The devices will be manufactured by Howmedica, Inc., instrumented by the Biomechanics Laboratory, Case Western Reserve University and inserted in a suitable patient population at University Hospitals, Case Western Reserve University. Loading data from the devices will be obtained over a six month period concurrent with external monitoring of patient activities at the Gait Laboratory, Case Western Reserve University.